Embodiments of the present invention relate to an X-ray system, an X-ray detector and, in particular, to an X-ray detector comprising an adjustable radius of curvature.
X-ray detectors, such as, for example, CCD sensors comprising scintillators, are included in X-ray systems in order to detect an absorption profile which results from transmission of an object by X-radiation and allows drawing conclusions as to a density distribution of the object.
FIG. 7 shows such an X-ray system comprising a radiation source 10 and a detector 12 which is arranged spaced apart from the radiation source 10 at a focus-detector distance a10_12. The detector 12 comprises seven detector modules 12a to 12g, such as, for example, seven detector lines. The radiation source 10, such as, for example, an X-ray tube, represents a point-shaped radiation source of an opening angle α14, the X-radiation emitted consequently propagating conically (see light path 14). Since the detector 12 used here is flat, an angle of incidence of the X-radiation (see light path 14) on the detector 12 is dependent on the place of the detector (cf. detector modules 12a to 12g). Thus, a central ray from the radiation source 10 impinges on the detector center or central detector module 12d perpendicularly, whereas the X-radiation impinges on the detector 12 the flatter, the more distant the specific detector module, such as, for example, 12a or 12g, is from the center.
Compared to bent detectors, flat detectors, such as, for example, flat-panel detectors or in particular line detectors 12, excel by their relatively low price and easy manageability, exemplarily with regard to variability of the focus-detector distance a10_12, wherein the image quality, however, may decrease towards the edge regions. This is due to the fact that the portion of the X-radiation 14 crossing a neighboring pixel increases with an angle of incidence becoming flatter (exemplarily in the detector module 12a or 12g). Due to the oblique transmission through the sensor layer, the spatial resolution is deteriorated or, more precisely, a signal is blurred over neighboring pixels. Consequently, this effect is maximal at the edge (cf. detector module 12a or 12g). Another effect is caused by the setup shown of a point-shaped radiation source 10 and a two-dimensional detector 12, namely the fact that different dose rates result from the different distances between the radiation source 10 and the detector modules 12a to 12g. Due to the greater distance, the dose rate on the detector modules 12a and 12g in the edge region is smaller compared to the dose rate on the detector module 12d in the center, resulting in a lower signal and, thus, higher noise (lower signal-to-noise ratio).
Additionally, it is to be mentioned that, with bent detectors (in contrast to flat detectors), as are exemplarily used in gantry systems, the angle of incidence is location-independent or even perpendicular when the focus-detector distance a10_12 (i.e. the distance of the tube-detector system rotating around the object to be measured) is not changed. In particular in industrial applications in which the measuring conditions (such as the positioning of the radiation source 10 relative to the detector 12) change frequently, bent detectors, however, are hardly used due to the invariable focus-detector distance a10_12.